Step 1Heat the oven to 375 degrees. Mix together half of the egg, buttermilk, vanilla extract and grated lemon zest in a medium bowl.
Step 2In a large bowl, sift together the flour, baking powder, baking soda, salt and the sugar. With a pastry cutter or fork, cut the butter pieces into the flour until the mixture resembles coarse cornmeal.
Step 3Gently fold the blackberries into the flour mixture, then add the buttermilk mixture, carefully stirring to avoid breaking up the berries until a loose, soft dough forms.
Step 4In a small bowl, whisk together the remaining half of the egg with the heavy cream; set aside. Using an ice cream scoop or measuring cup, scoop out rounded one-fourth cup portions of dough onto a greased baking sheet about 1 1/2 inches apart. Brush each of the scones lightly with the egg-cream mixture (you will not use all of it) and sprinkle each with a little of the coarse sugar. Bake 30 to 35 minutes until the scones are puffed and the tops are golden brown. Makes 1 dozen.